Hydraulic propeller pitch-changing system



June 2, 1953 M. E. CUSHMAN 2,640,555

HYDRAULIC PROPELLER PITCH-CHANGING SYSTEM Filed March 1, 1946 7 Sheets-sheet 1 June 2, 1953 M. i-:. CUSHMAN I 2,640,555

HYDRAULIC PROPELLER PITCH- HANGING SYSTEM Filed March 1, 194a 7 Sheets-Sheet 2 V INVENTOR. Mad/ 56E Gus/z rm/z ATTORNEY INVENTOR. Mantel; Cusfimazz BY a 2 7 Sheets$heet 5 ATTORNEY llllllllllllllllllllllllllllllllll'l-lll I.

June 1953 M. E. CUSHMAN HYDRAULIC PROPELLER PITCH-CHANGING SYSTEM Flled March 1 1946 June 2, 1953 M. E. CUSHMAN 2,540,555

HYDRAULIC PROPELLER PITCH-CHANGING SYSTEM Filed March 1, 1946 v '7 Sheets-Sheet 4 I N V EN TOR. Maui [661: Cusma/Z A I'OKNL'Y June 2, 1953 M. E. CUSHMAN HYDRAULIC PROPELLER PITCH-CHANGING SYSTEM 7 Sheets-Sheet 5 Filed March 1, 1946 June 2; 1953 M. E. cUsHMAN HYDRAULIC PRQPELLER PITCH-CHANGING SYSTEM Filed March 1, 1946 7 Sheets-Sheet 6 1 N V EN TOR.

K .flfau z ital Cus/zmmz M. E. CUSHMAN HYDRAULIC PROPELLER'PITCH-CHANGING SYSTEM June 2, 1953 7 Sheets-Sheet 7 Filed March 1, 1946 INVENTOR.

BY Mala/"(ME (us/Imam ZATTOKNEY Patented June 2, 1953 HYDRAULIC PROPELLEB PITCH-CHANGING SYSTEM Maurice E. Cushinan, Verona, N. J., assignor to Curtiss-Wright Corporation, a corporation of Delaware Application March 1, 1946, Serial No. 651,264

Claims. (Cl. 170-16031) This invention relates to aircraft propellers and is concerned with a novel form of controllable pitch propeller hub and blade organization along with a novel control system for th propeller.

In general terms, the invention includes a propeller blade mounted in such fashion that the centrifugal blade twisting moments tending to turn the blades toward zero pitch position in operation are compensated by the effects of centrifugal force on the blades whereby the effort necessary to turn the blades for pitch change is only that needed to overcome friction and discrepancies in compensation due to manufacturing allowances. The pitch changing motor is hydraulic and by virtue of the small amount of force required to change blade pitch, may operate on hydraulic pressures much lower than those conventional in prior practice. The propeller further includes a simple mechanical control system which permits propeller operation, in the normal governing range, for feathering, and in the reverse pitch range. .In addition, the propeller is capable of automatic constant speed governing during reverse pitch operation. A high rate of pitch change is automatically attained when transition from normal pitch range to feathering and reverse pitch is selected, the high rate of pitch change also being automatically attained in the return from reverse pitch operation.

Objects of the invention are (a) to provide a propeller whose control system has full flexibility through a considerable number of different operating ranges; (b) to provide a hydraulic propeller capable of operation at relatively low hydraulic pressures; (c) to provide a propeller which is Wholly seli-containcd so that no special provisions are required in the prime mover for propeller operation or control; (d) to provide a propeller control system wherein a single hydraulic valve is controllable to provide high and lowpitch change rates and is influenced by several mechanical. controls to fulfill its several operating functions; (6) to provide a highly flexible propeller system which is simple in operation-and simple in structure, so that minimum servicing and operational difficulties are likely to be encountered in its use.

The above and additional objects which will become apparent are accomplished by the structure and arrangement set forth in the following detailed description when read in connection with the accompanying drawings. It is to be especially understood, however, that the drawings-are merely for the purpose of illustration and are not to be construed as a definition of the limits of the invention, referenc being had to the appended claims for this purpose.

In the drawings, wherein like parts are designated by like reference characters,

Fig. 1 is a longitudinal section through the prop ller-hub;

Fig. .2 is a section on the line 2-2 of Fig. 1;

Fig. '3 is a section on the line 3 3 of Fig. .1;

Fig. 4 is an enlarged fragmentary view of a portion of the pitch changing mechanism;

Fig. 5 is a schematic diagram showing the propeller control system adjusted for normal governed propeller operation;

Fig. 6 is a schematic diagram showing the propeller and controls in the feathering position; and

Fig. 7 is a schematic diagram of the propeller control system adjusted for reverse pitch operation.

Reference may first be made to Figs. 1 through 4 showing the propeller structure. Therein, a propeller hub i6 is provided with a plurality of blade sockets .H and with a' cylindrical rearward extension 12. This extension provides internal mounting points it and ii, the latter comprising a spline connection, for securing the propeller hub to a power shaft l5 extending from the driving end It of any suitable prime mover.

Propeller blades ll of any suitable construction are removably mounted in the blade sockets .l I, the butt of eachblade havin a recess 18 engage by a pair of half-rings 19 which likewise engage a lower race having .a spline connection "2| with an adapter 212, which is splihed in turn'to the propellerblade butt at'ZB. The blade, adapter 22, race .26 and split ring 19 are secured together by a nut z l. Loosening of this assembly allows removal of the retaining rings I9 and then removal of the blade ll irom the retaining structure. The adapter 22 carries a spur gear segment .325 (Fig. '3) whose purpose will become apparent.

The -lower race [2t rests upon a Belleville Washer .2 6 at its inner portion, through a thrustballbaring 27, the outer rim of the washer 2t resting upon a shoulder 28 formed in the blade socket N.

This washer limits inward bl de m e n an provides a preload on the blade retention at all times.

The upper surfac of the l wer IflCBZE i f e withfloam profile as disclosed in my l o-pending app cation entitled v ri 'b Pitch P p l e Serial-N0. 598,792. filed June 11. 194. n wU- Pat. $2,533,358 issued onpecember 12, 1.959; and S ri l N0-I59B,7 .1 filed June .11, 1. 0W U- S- Pat nt .No. 2.51M?? iss e on Ju y .19 0- A plurality of rollers 38 bear upon the upper surface of the lower race 20, and these rollers in turn engage an upper race 3! also having cam profile in accordance with teachings of said applications, which is screwed as at 32 into the outboard end of the blade socket H, the race 31 being secured from rotation in the socket by lock keys 33 fastened by screws 34. The rollers 30 are held in a cage 35 whose motion relative to the races 20 and 3| is controlled by pinions 315 meshed with gears 31 and 38 formed respectively on the outer edges of the races 20 and 3!. The cams and rollers above mentioned are so constructed as to provide a twisting moment on each propeller blade shank equal and opposite to the twisting moment resulting from the outer portions of the propeller blade which tend in operation, in a manner well known in the art, to move toward a flat pitch position.

In the blade and hub construction above described, the propeller blade I! will have a slight radial movement with respect to the propeller hub during pitch change and this radial movement results in varying deflections in the Belleville washer 26. With the indicated radial movement, the spur gear 25 also moves.

To provide for sealing within the blade socket, a member 40 is formed in the propeller hub whose outer end loosely engages the bore of the adapter 22, and is sealed thereto by a ring seal 4!. Ring seals 42, 43 and 44 are further provided in the hub structure to eliminate fluid leakage from the hub. The seal 43 is of such character as to permit pitch changing rotation of the propeller blade I! with respect to the upper race 3| without loss of fluid within the hub.

The front end of the propeller hub is provided I with a closure 45 sealed as at 46 and 41 to the hub, the opening through the element 45 permitting free passage from the front of the hub into the hollows of the propeller blades should the propeller system be equipped with a hot gas de-icing system. The opening through the element 45 further provides access to the propeller hub lock nut assembly, not shown, by which the j propeller hub is secured to the prime mover shaft I5.

Embracing the rear cylindrical extension i2 on the propeller hub is a cylinder 50, there being an annular cylindrical space between the extension I 2: and the cylinder 50. Within this an- V nular space is an annular piston capable of longitudinal sliding movement between the elements [2 and 50. This piston defines forward and rearward annular spaces 52 and 53 respectively whose purpose will shortly become apparent. The cylinder 50 is stationary-that is, it does not rotate with the propeller. To hold it from rotation, the rearward end of the cylinder 50 is provided with a flange 54 secured to a cylinder-embracing housing 55 and to a reaction plate 56 by screws 5?. The plate 56 carries a rubber ring 58 having openings 59 engageable with dowels 60 secured to the prime mover nose "5.

cylinder and housing assembly including the ele- 4 ments 50 and 55 will be removed with the hub, the rubber ring 58 merely slipping from the dowels 50. Also, during propeller operation, the fixed and rotating parts of the propeller are held in fixed axial relationship.

The closure 62 is sealed to the hub extension 12 by a ring seal 65.

The hub H) at the front end of the extension 12 carries a plate 61 which is sealed to the hub by a ring 68 and is secured to it by screws 69. Said plate forms a forward closure for the annular space 52. Said plate includes a rearwardly extending flange I6 which carries a metallic seal ring H bonded thereto and integral bevel gear 72. Engaged with the ring seal 1| is a stationary coacting seal ring 13 slidably fitted to a recess 14 in the housing 55, said ring 73 having a resilient sealing annulus I5 engaging the recess 14, and said seal ring 13 being urged axially into contacting engagement with the ring 1| by awave spring '26 between the ring 13 and the housing 55. Thus, the annular contact surface between the rings H and 13 provide a rotating seal capable of sustaining hydraulic pressure without substantial leakage. A bushing l! is fitted to the flange ID to provide a radial bearing for the forward end of the cylinder 50, supporting the latter and the housing 55.

A passage 78 around the bushing 11 leads from the forward annular cavity 52 to the clearance space between the cylinder 50 and the ring seal assembly just described and this passage communicates as shown in Fig. l, with a fluid feed passage 19 which serves .as an entrance and exit for fluid flowing to and from the forward annular cavity 52. The rear annular cavity 53 receives and discharges hydraulic fluid through a passage 58 shown in Fig. 1 formed in the housing 55 and in the cylinder 50.

In addition to the rotating sea-l provided between rings H and 13, additional sealing provisions are incorporated in the hub end of the piston-cylinder assembly, these including a seal ring 82 disposed between the housing 55 and the plate flange Til, and secured in position in the plate flange H! by a fitting 83 secured to the plate flange. A recess 84 is defined between thefitting 83 and the housing 55 which accumulates minor leakage from the rotating seals H, 13 and 82 whence leakage fluid is returned to a fluid sump, not shown, through a duct 85. Between the ring seal ll-J3 and the ring seal 82 the housing 55 is provided with a drain duct 86 which returns leaked fluid to the sump.

At the rearward end of the piston-cylinder assembly the closure 62 is provided at its outer rim Witha, piston ring seal 88 disposed in a groove 89 in the closure. This ring normally bears upon the inner surface of the cylinder 50, but is free to move axially relative thereto. Rotating engagement will occur between the ring 88 and the surfaces of the recess 89 and this arrangement will provide a primary seal for fluid within the annular cavity 53. Such fluid as may leak past the seal 88 will be returned to the sump through a passage 90, (Fig. 1). Some fluid will reach the axial restraint structure involving the elements GI, 62 and 63 and any fluid leaking past this structure will be returned to the sump through the drain passage 9| shown in Fig. 4.

As will be noted in Fig. 1, the oil feed passages 19 and to the cylinder 50 pass through the housing 55. This housing may have slight clearance relation with respect to the exterior surface of the cylinder 50 and accordingly, seal rings 92 and 93 are provided between the housing 55 and the cylinder 50 to prevent interflow of pressure fluid between the passages 19 and 80 and to prevent leakage ofv fluid from the passagev B to the exterior of the housing structure.

Referring now to Figs. 1 and 3, means are shown by which axial movement of the piston I, under the influence of hydraulic pressure on either side of the piston, causes propeller blade pitch change. The piston 51 has adjustably secured thereto a number of rods t5 equal to the number of propeller blades. Each of these rods projects forwardly through an opening in the rear wall of the propeller hub as at 96 and is formed, at. its forward end, as a. gear rack 91 engaging the spur gear secured to the blade butt. Opposite the engagement of the rack teeth with the gear 25., a back-up bearing 98 is provided in the hub structure, this bearing serving to hold the rack teeth in close engagement with the gear teeth to prevent backlash and bending of the piston rod.

In its passage through the rear wall of the propeller hub, the piston rod 95 is provided with a packing Hill to suppress excess leakage of hydraulic fluid from the annular cavity 52 into the propeller hub proper. The hub, being sealed by the various seal rings. and :packings previously mentioned, is intended to operate substantially full of oil. When the hub is full of oil, and should the piston 51 be in a right-hand position as shown in the drawings, there will be maximum volumetric space in the hub, which is filled with oil. Now, if the piston should be moved leftwardly, the piston rods 95 will occupy some of the free space within the hub and. will displace fluid therefrom. To provide for bleed of such fluid from the hub, a check valve M32- is, provided which will allow outflow of oil from the hub to-the annular cavity 52. It will be apparent that upon piston movement tothe left, pressurev will be on the right side of the piston 5| so that the annular cavity 52 is in an unpressurized condition. If rightward movement of the annular piston 5! is enforced by applying fluid pressure in the annular cavity 52, the check valve I02 will close, the piston rods will be withdrawn to some extent from the hubinterior, and some additional clearance space will. then be provided within the hub which in due course, may receive oil leakage from. the annular cavity 52. through the seals. I00.

Regardin the piston 51, a seal ring packing I-M is provided in its bore, for sliding andsealingengagement with the outside of the. cylindrical portion of the hub (l2). The piston slides but does not rotate with respect to this cylindrical hub portion. The outer rim of the piston as best shown in Fig. 4, is providedwith apistonring groove I 05: to which. is fitted, a split. piston ring Hi6 which springs outwardly into engagement with the cylinder 50 for; sealing, engagement therewith. This piston ring. may have. a non- -meta1lic seal ring I01 set into. an. appropriate groove in its'outer surface. Since. the cylinder 51] is stationary, and since the piston 51 andthe cylinder l2- rotate, the piston ring. N161 willhave non-rotating sliding engagement with the. wall or the cylinder 50 and relative rotation will'occur between the piston ring. and the piston 51. The sealing surfaceswillbe the side wallsof'thelpiston ring Hit and the-side wallsof thegroove 165 in the. piston.

Summarizing the operation. of. the structure thusfar. described, the cylinder. 50 and the housing 5,5.secured thereto are held, stationary by. the

engine nose dowels 60, while the propeller hub",

the extension l2, and the piston 5| rotate as a unit. 'Upon admission of pressure fluid to the rear annular space 53 through the passage 80, the

piston 5| will be moved forwardly, and the several racks 9! will thus cause anti-clockwise movement of the propeller blade about their own axes, moving the propeller blades into a high annular space 52 from the passage 19, the piston 51 is moved rearwardly causing pitch decreasing movement of the propeller blades. In the embodiment shown, the range of pitch angle adjustment of the propeller blades is approximately 120. degrees, allowing a full degrees of positive pitch positioning ofthe blades, and 30' degrees of negative pitch positioning. of the blades. When the piston 5| is in its rearward-most position, the propeller blades will be in negative or reverse pitch position.

Should a propeller be desired with the pitch changing range limited to high and low pitch respectively less than. 90 degrees positive pitch and more than. zero pitch, the extension [2 and its associated structure may be shortened, and a different means may be used for translating movements of the piston. 5 l. to blade pitch-change. For instance, connecting rods ivoted to theblade butts and piston rods, or slotted bars on the piston rods engaging, pins on the blade butts, could replace the rack 91 and the gear 25. In the propeller described, relatively low hydraulic pressures are needed to. cause blade pitch changes even at a high. rate, due tov compensation of blade centrifugal twisting forces. Such pressures may reach a maximum. of 600 p. s. i. but normally'will be much lower. When not changing pitch, fluid pressure in the propeller actuating-cylinder will be very low. v

While any suitable means may beuse'd to control the application of pressure fluid to the passages. War at in the fixed housing 55, to efl'ecti the desired range of blade pitch changes or to effect governing off the propeller blade pitch, I have shown one: embodiment of a pitch control system to allowhighly flexible propeller pitch control under various conditions of propeller operation. Such a control system is shown'in' Figs; 5, Grand 7.

Fig; 5 shows the essential elements of the control system, and the'system adjusted for normal automatic governing operation of the propeller. The gear 12 rotating with the propeller drives a bevel. pinion H ii, the hub of which is formed as a cup to contain a plurality. of. flyweightsi I H pivoted on axes parallel to tangents to. the pinion so that they may swingv inwardly andoutwardly in responseto. speed changes of the propeller. Each flyweight carries an arm H2 which: bears upon a fiange. l l3 of the plunger H4 piloted in the shaft H5 of the pinion. As schematically shown, the pinion=shaft I I5; drivesa pump [6-, preferably of gear type, which is fedfrom a pipe 1 I! lea-dinghto asump, not shown. Pressure fluid delivered by the pump H6 whilethe latter-is rotating due: to propeller rotation is deliveredto a pipe-H8 The pipe I [8 leads to an'unloader valve assembly H9 andthence through a pipel201:0thecentralpumtion of a valvebo'dvlil. Thepipei20 'alsodeads through a cutoff valve I22 to an accumulator or air bell I23. 4

The unloader valve assembly I I9 includes a check valve I25 permitting fluid flow from the pump to the line I20. An additional valve I26 is connected to the line I I8 and when the valve element I21 is off its seat, fluid delivered by the pump is dumped to the sump through the line I28. A differential pressure valve I29 is fed from the line I28 as at I30, the line I30 normally being closed by the valve I3 I backed up by a spring I32. When pressure in the line I30 is sufiicient, the valve I3I will move from its seat, against the spring I 32, said valve seating on a larger diameter seat as at I33. Thereupon, fluid pressure in the line I20 is transmitted to a small cylinder I34, containing a piston I which may move leftwardly to open the valve I25. The valve I3I, in seating against the seat I33, prevents loss of fluid from the line I20 to the sump. When the pressure in the line I20 drops to a value less than the unit pressure determined by the load of the spring I32 and area of the valve seat I33, the valve I3I will move to the right to seal the pipe I30. Then the cylinder I34 will unload to the sump, the valve I21 will close, and the pump IIfi will again be pressure loaded to provide fluid to the system. This unloading system, just described, serves in conjunction with the accumulator I23, to maintain fluid pressure in the line I20 but allows the pump III; to be unloaded when fluid demand is not present or when the accumulator I25 can supply the fluid demand.

The flange I I3 of the flyweight governor forms an abutment for one end of a lever I38, fixedly pivoted at I39, the other end of the lever bearing on a stem I which enters the valve housing I2I, said stem bearing downwardly upon a valve I4I within the body. The downward pressure exerted by the stem I is a function of the R. P. M. of the propeller, and in normal governing operation is counteracted by a speeder spring I43 bearing upwardly upon the bottom of the valve MI The force exerted by the speeder spring is adjustable through an abutment I44 carrying a rack I45, the

abutment I44 being moved axially by a cable or other suitable connection I46 connecting the rack pinion to a speed adjusting control I41. If the control I41 is moved leftwardly as shown, the abutment I44 will be raised, compressing the spring I43, raising the valve MI and the stern MI}. As propeller speed increases, a balancing force from the governor will neutralize the position of the valve I4I.

The valve body I2I is provided with axially spaced ports I49 and I56, connected respectively by pipes bearing the same numbers to a flow reversing valve I5I. In the normal automatic governing position shown in Fig. 5, a pipe I52 communicates with a pipe I and with the passage 50 in the propeller annular cylinder, permitting hydraulic fluid to pass to the annular space 53. The pipe I49 in the normal position shown connects with a pipe I53 leading to the leftward end of the accumulator valve I22 and thence through a pipe I54 through the passage 19 connecting with the annular space 52 in the propeller operating cylinder.

enter the annular space 53 to cause increase in pitch of the propeller. In this position of adjust- .ae opcc ment, the flange I55 uncovers the port I49 so that fluid in the annular space 52 of the propeller passes through the several pipes I54, I53 and I49 to a dump pipe I58 connected to the sump indicated by the letter S. This position of adjustment represents a demand by the governor for increasing propeller pitch. If the governor demand indicates a need for decreased propeller pitch, the valve MI will raise to a position where the pressure line I 20 connects to the line I49, and where the annular space 53 connects, through the lines I52 and I50, to the sump, through a dump pipe I59.

If transient changes occur in propeller R. P, M., the flyball governor assembly in the pinion IIO wil effect hydraulic control of the propeller toward increased or decreased pitch positions to bring R. P. M. of the propeller to an equilibrium condition. If purposeful changes are made in the R. P. M. setting desired, by manipulation of the control I41, the valve MI will vary in position to allow increase or decrease of propeller pitch to the newly set R. P. M., culminating in balance of forces between the speeder spring I43 and that exerted through the stem I40 by the iiyweight action of the governor.

There is no provision for a high pitch limit in the propeller during normal governing operation. There is. provision for a normal low pitch limit, incorporated in a cam cylinder I (H secured within the stationary housing 55 and turned, through a shaft I62, by a flexible strap H53 having a shoe I54 bearing at times upon the rear face of the annular piston 5L A torsion spring 555 is provided to urge the cam cylinder 66! in a direction to enforce strap movement toward the piston and the position of the cylinder I5I is established by the abutment of the shoe I04 on the piston 5I. A connection may be made if desired from the cylinder I51 to a pitch indicator I65 so that the operator may note at any time the pitch position of the blades. Such an indicator may also be used to operate auxiliary controls requiring pitch sensing devices. If the piston moves to the rear as shown in Fig. 5, the cylinder IGI will be turned so that a cam lobe I51 thereon engages a follower I59. having a fixed pivot I65 As the propeller approaches low pitch, the cam I61 will raise the follower I58. This, in turn, raises a lever I10, fixedly pivoted at HI, and causes the right hand end H2 of the follower to descend. This follower end I12 is engaged with a pull rod I13 passing through the speeder spring abutment I44 to a button I14 engageable at times with a thimble I15 which forms the top abutment for the speeder spring I43 and which further bears'upon the valve I4I. As the cam I51 raises the follower I 68, the speeder spring, through the mechanism just described will be retracted, to the amount necessary to cut off fluid flow to the port I45, preventing further pitch change in the low pitch direction.

If increased pitch (or decreased R. P. M.) is called for by the governor flyweight, the valve I -II will descend with respect to the button I14 under the influence of the force from the governor, permitting pressure fluid to pass to the propeller cylinder annular space 53 for pitch increase. As pitch increases, the eifect of the low pitch cam I61 drops out and the propeller resumes normal governed operation.

Now, reference may be made to Fig. 6 which shows the position of adjustment of the system for propeller feathering. Selection of propeller feathering is made by a control I13 which is moved forwardly to the feather position (F) from the prior normal position (N). Through a mechanical connection such as a cable ill), the control lit moves a member i681, fixedly pivoted at It to the stationary housing 55, in a counterclockwise direction. The member lilo carries a disc segment I82 having a shoulder i815 which will be turned by manipulation of the control to engage a finger i8 3, turning the finger in a clockwise direction about its fixed pivot Hi and against a centering spring we. This spring holds the finger Hi l in a normally horizontal position, but allows it to be tilted up or down by the shoulder or by other means to be described. To the finger 184 is secured a cam I81 having a central low point I88 bordered by high points and lllll. The cam follower 168 has a roller follower iSl normally bearing upon the cam lt'i. In the normal central position or" the adjustment of the finger its, shown in Fig. 5, the roller it! rests upon the low point its of the cam but in the feather position, when the finger Hill is depressed, the roller iti raises to the high point 89 of the cam. With this movement the follower i558 raises the member l'iil against a return spring 3532 and enforces downward movement of the stem H3 and the button lit. With this action, the speeder spring M3 is compressed, retracting the thimble lib clear of the valve ldl. This allows the valve l ll to drop, connecting the fluid pressure line l2il to effect pitch increase of the propeller at a high rate of change, by passing fluid to the annular space 53. There being no normal high pitch limit stop, the piston 5i will move leftwardly to increase propeller blade pitch until the piston 5| abuts the front end of the annular cylinder formed by the elements l2 and 55. The relationship of the piston rod 95 to propeller blade angle is so adjusted that the propeller blade will be in a full feathering position as shown when the piston abuts'the cylinder.

When the control lid is moved to the feather position, the disc segment H32 was moved counter-clockwise and another shoulder i955 moved away from an arm let of a bellcrank having a fixed pivot l98. The otherarm 398; of the bellcrank moved away from a plunger 2% associated with the accumulator shut-off valve 122. This valve comprises a body having central ports with which the pipe I26 and the pipe leading from the accumulator I23 communicate. A piston 29! is slidable in the valve body from a position such as is shown in Fig. 5 where the pipe 12c and the accumulator-are open to eachother, to a position shown in Fig. 6 where the pipe i253 and the accumulator pipe are sealed off. The piston 20! is operated by a plunger 2G2 having an operating button 2% at its left hand end for engagement by the arm we of the bellcrank N31. The plunger 282 has a secondary piston 285 between the accumulator port and the left end of the valve body, said left end being ported to receive the pipe ltd from the front end of the propeller operating cylinder and the pipe joining the valve I22 with the reversing valve It i. In the normal position, the plunger 2% is held in a rightward position by the bellcranl; till. When the control H8 is moved to feathering position, the bellcrank moves away from the plunger button 2% so that the latter is free to move to the left under the influence of a light spring 29?. During the feathering cycle, fluid in the annular space 52 of the propeller operating cylinder-is driven from it, through the pipe ltd and through the left end of the .valvev i22. While fluid is flowing there will be back pressure due to line drop bethe valve Nil.

tween the valve are and the sump exerted against the left side of the piston 26%, holding the plunger its and the piston Bill in the right. hand position. As the propeller blades approach the feathering position, the rotational speed of the propeller diminishes with attendant slow down in delivery from the gear pump. H6. 'As the pump output diminishes, the pressure avail-. able in the accumulator will provide the power for completing the feathering cycle, by delivering fluid to the pressure line I26. As the propeller blades reach the feathered position, flow of liquid from the annular cavity 52 will cease and pressure in the line 154 will accordingly drop on" to a negligible value. Thereupon, the spring no"! will move the piston. ill leftwardly, since the bellcrank li l no longer holds the plunger 2M, and the accumulator willbe sealed off by the piston 286. At this point, the whole system bee comes static.

During the feathering cycle, propeller pitch change at a very high rate is accomplished since the speeder spring M3 has been retracted and a full opening of the ports M9 and IM ispermitted. To aliord a uniform high rate of pro peller feathering, the valve body I2! is provided with an auxiliary spring 289 having a fixed abutment at its lower end and bearing on a washer 2H its upper end. The washer has an upwardly limited movement established by a shoulder 2H in the valve body l2! which is so placed that when the valve flange I56 rests against the top of the washer 2MP, the port 158, will be partly open. With the Speeder spring retracted, further downward movement of the valve Mi can be affected, and the opening of the port Hit can be increased by the valve flange 156 bearing down on the auxiliary spring 209. Such movement will be roughly proportional to the downward force on the valve Ml which is a function of propeller speed. With variations in this force, the valve it! may move slightly up and down, altering the area of the port I53 to provide pressure on the downstream side thereof which will be suflicient to maintain a constant high rate of pitch change.

When unfeathering is desired the control I18 is moved from the feathering position to the normal position (N). This action turns the disc segment I82 in a clockwise direction, permitting the finger i8 5 to resume its normal horizontal position. This places the roller 19! in the low notch [88 of the cam I81, releasing the governor valve Speeder spring M3 so that it may influence Concurrently, the bellcrank I91 will be turned counter-clockwise, the crank arm lSll pressing on the button 203 and forcing the piston 2M to a rightward position against the spring Eii'l. Thereupon, pressure fluid from the accumulator M3 is admitted to the pressure line 52%) so that it may enter the valve housing 12!. Since the propeller is stopped, there is no downward force from the governor on the stem I40, and the Speeder spring [43 is pressing the valve Ml upwardly. Thus, the pressure line I2!) is placed in communication withthe port I48 and pressure fluid flows therethrough, through the reversing valve Hi, the accumulator valve in, the pipe 154, to the passage l9 and the annular space 52 forward of the propeller piston 5 I. This causes rearward motion of the piston and move ment of the propeller blade toward a low pitch position. The propeller will then begin to wind:- mill and as it picks up speed, the gear pump i l-,6 will begin to develop pressure to carry on the unfeathering operation until the system resumes 11 its normal mode of operation for automatic speed governing, as previously described in connection with Fig. 5.

Fig. '7 shows the control system in one of the phases of revers propeller pitch operation. As is known in the art, reversal of propeller pitch is useful to provide aerodynamic braking of an aircraft, either during landing operations or for dive braking. A prime requirement for propeller pitch reversal is to have a very high rate of pitch change from normal to reverse pitch and from reverse pitch to normal so that engine overspeeding will not occur due to windmilling action, or due to a power-on condition of the en gine while it has little or no propeller load.

When th control I18 is moved to the rear, to the reverse pitch position (R), the disc segment I82 is rotated in a clockwise direction from normal about 90 degrees. A pin 2I5 on the disc I82 engages a slot 2l6 in a plate 2!? having a fixed pivot 2I8. As the disc I82 turns, the pin swings the plate 2|! through approximately 90 degrees and by its direct connection with a rotor 2H3 of the reversing valve I5I, th valve position is altered. 'I'hereupon, the pipe I 49 from the governor valve I2I is connected through the pipe I52 and the passage 80 to the annular space 53 in the rear end of the propeller cylinder. The pipe I50 is connected through the pipe I54 and the pas sage T9 to the annular space 52 at the front end of the propeller cylinder.

In turning clockwise as above described, the disc I82 carries a projection 22! co-planar with the finger I 84. As the disc I82 turns, the pro- J'ection engages the finger I84 moving it upwardly approximately 45 degrees. When so moved, a dog 222, rotatable with the finger, is engaged by a pawl 223, the pawl being mounted on a fixed pivot 224 and being urged into engagement with the dog 222 by a spring 225. This action locks the finger I84 in the upwardly tilted position, after the projection 22I has passed beyond the finger. With the finger turned from the horizontal position, the high cam surface I90 of the cam I 87 is moved under the roller I54, raising the follower I68 and forcing downward movement of th arm I12 and of the button il i. This compresses the speeder spring I43 in the manner previously described in detail, allowing full communication between the pressure line I20 and the pipe I50. Since the pipe I50 is now connected through the reversing valve to the front end of the propeller cylinder (the annular space 52) pitch decreasing movement of the propeller blade is enforced at a high rate of pitch change. Propeller blade pitch will pass through zero to the negative pitch region at high rate until the negative pitch limit is reached. This limit is established by a cam knee 22? on the cylinder IBI which, as previously described, rotates in accordance with the position of the an nular piston 5| and the propeller pitch changing mechanism. The knee 221, as the cylinder it! rotates, engages a leftward projection 228 of the pawl 223, raising said pawl from the dog 222 and allowing the finger I84 to resume its normal horizontal position. This restores the roller I9! of the follower I68 to the low point on the cam I87, allowing the speeder spring I 43 to expand and to resume its normal function. Fig. 7 shows the system after the reverse limit stop has been reached wherein the control of propeller pitch has been returned to the governor. The governor will now control the speed of the propeller by adjusting pitch, in the reverse sense, to maintain constant engine speed.

During this reverse pitch operation, the pump IIS and the accumulator I23 serve in their normal fashion to provide pressure fluid to the line I20, and the governor valve MI will move in response to governor action and Speeder spring force to adjust propeller pitch. The cam Ifila on the cylinder IBI provides, as shown in Fig. 7, a low negative pitch limit stop, operating in exactly the same way as this cam operates for low positive pitch limiting. High negative pitch is limited by the piston 5| mechanically abutting the rear of the propeller actuating cylinder.

When it is desired to return from reverse pitch operation to normal operation, the control I18 is moved to the normal position (N). This action swings the disc segment as; counterclockwise from the Fig. 7 position through about 90 degrees to the position shown in Fig. 5. The pin M5 on the disc I82 swings the plate 2Il and restores the reversing valve rotor 2I9 to the position of Fig. 5, thereby establishing com munication from the governor valve port I59 through the pipe I54 to the annular space 52 in the front end of the propeller piston, and establishing communication from the governor valve port I55 through the pipe I52 to the annular space 53 at the rear end of the propeller cylinder. Concurrently, the projection 22I on the disc I82 moves downwardly, engaging the finger I84 and moving it downwardly and clockwise to about 45 degrees below the horizontal. This turns a dog 232 to allow a pawl 233 to engage the end of the dog and to hold the finger I84 and its associated parts in the clockwise tilted position. In the meanwhile, the projection 22I has passed beyond the finger I 85 to the position of Fig. 5. With the finger Hi4 tilted downwardly, the roller IQI of the follower I58 has been raised to the high point ice of the cam I81. This has the same action as previous ly described in compressing the speeder spring I43 and in allowing virtually full opening of the port I50 in the governor valve so that pressure fiuid may flow from the line i253 through the lines I50 and I52 to the annular space 53, urging propeller pitch increase in a positive direction at the high rate of pitch change previously described in connection with the feathering cycle. As the propeller blades reach a pitch position within the governing range, a cam knee 235 on the cylinder I6I comes into contact with an extension 236 of the pawl 233, raising, said pawl from the dog 232 and allowing the finger I84 to resume its normal horizontal position. Thereupon, the roller I9I of the follower I58 drops to the low point of the cam I8! and control of propeller pitch is returned to the flyweight governor and the speeder spring I43. As indicated previously, the cylinder IBI moves in response to position of the propeller piston 5I. It is preferred to fit the cam knee 235 on the cylinder I 6| at such a position that unreversing of the propeller will terminate within the normal governing range. This assures faster restoration of the system to normal governing action than is aiforded when the terminal of unreversing is at the normal low pitch stop. The propeller pitch can then readjust itself from the terminal position of unreversing either toward high pitch or low pitch as the governor may demand. In the case of installations for dive braking, the unreversing terminal position will be toward the high pitch end of the normal governing range to minimize overspeed ing tendencies; for ground braking, such terminal position will be toward the low pitch end of normal governing in preparation for full power takeoff. The several cam elements H57, 227 and 235 are relatively angularly adjustable on the cylinder it i, so that changes may be made in the limit positions as desired.

While the specific cycles of propeller operation have been described above in conjunction with the various mechanisms, a summary will be given of some of the more outstanding and significant points which flow from the practice of this invention. Save for the simple reversing valve I51, the relatively standardized unloader system its and the accumulator shutoff valve I22, all control of the hydraulic fluid for all of the various regimes of operation or the propeller are concentrated in the governor valve l2i. While this valve under ordinary circumstances is controlled purely by the propeller governor fiyweight and the speeder spring Hi3, it is biased by the mechanisms controlling different regimes of operation to yield both a low rate of pitch change proportional to the offspeed condition and a high uniform rate of pitch change for feathering, reversing and return from reverse. This not only simplifies the hydraulic system materially but has the attendant advantage of reducing potential sources of fluid leakage. In other hydraulic control propeller systems known in the art, a large number of valves are required to alter fluid circuits in such fashion that high and low rate pitch change may be accomplished. Virtually all of the control mechanisms shown in Figs. 5, 6 and 7 are, physically, incorporated in the stationary housing 55 secured to the rear portion of the propeller. Exemplary of this, Fig. 4; shows the disposition of the flyweight system in said hous ing. The oil sump mentioned heretofore, while not shown, is merely an appropriate cavity located in the stationary housing 55. The only part of the system not incorporated in the propeller or in the stationary housing 55 is the speeder spring adjustment involving the control i l-l, and the function control for feather, normal and reverse pitch operation involving the control 578. The housing 55 may contain additional apparatus, or some of the apparatus described may be replaced, to provide special control functions needed in connection with different types of prime movers such as conventional engines or turbines, and may further be modifled to include synchronizing equipment used for multi-propeller or multi-engine installations in the aircraft.

Though but a single embodiment illustrating the invention has been illustrated and described, it is to be understood that the invention may be applied in various forms. Changes may be made without departing from the spirit of the invention as will be apparent to those skilled in the art, and reference should be made to the appended claims for a definition of the limits of the invention.

What is claimed is:

1. In a propeller for aircraft having a hub and blades journalled in said hub for pitch change, a rearward cylindrical extension on said hub, a plate at the forward end of said extension secured to said hub, a cylinder coaxial with said extension and defining therewith an annular cylindrical chamber, the rearward end having a closure in rotary sealing relationship with a rearward portion of said extension, a rotary seal between the forward end. orsaid cylinder and said plate,

with said extension and rotatable and sliding sealing engagement with said cylinder, a plurality of driving means connecting said piston with the blades of said propeller comprising rods secured to the piston and passing through said plate and hub whereby axialpiston movements cause pitch changing blade movements in said hub, and means wholly carried by said cylinder to admit hydraulic fluid to the ends of said cylinder for moving the piston in an axial direction therein, said last named means comprising a governor driven by the hub having a fluid regulating valve and means to overcontrol said governor valve responsive to the position of said piston with respect to said cylinder.

2. In a controllable pitch propeller comprising a hub and blades mounted therein, a pitch changing motor comprising a piston rotatable withthe propeller, a stationary cylinder within which said piston is slidable, means mounted on said cylinder but movable by said piston, whose movement is a function of blade pitch angle, pitch limit stops for low pitch, feathering and reverse pitch, and means responsive to said movable means to control said low pitch, feathering and reverse itch limit stops.

3. In a propeller for aircraft comprising blades journalled in a hub, said hub including a coaxial cylindrical portion, a nonu'otating cylinder embracing said portion, means providing a rotating seal between each end of said cylinder and the ends of said portion, said mean providing c10- sures at the ends of said cylinder, an annular piston within the cylinder embracing said cylindrical portion and slidable therealong, said piston being rotatable with said cylindrical portion and having rotating clearance with the wall of said cylinder to allow of relative rotation therewith, rotating seal means disposed on the rim of said piston engaging the wall of said cylinder to afford a fluid seal between the piston and cylinder, a plurality of rods secured to said piston and passing through the hub for connecting said piston with said blades whereby axial piston movement imparts pitch changing movement to said blades, fluid supply pressurizing and control mechanism carried by said cylinder, means controllably operative to direct pressurized fluid from said mechanism to one end or the other of said cylinder to move said piston axially within said cylinder, a pivot secured in one end of said cylinder in a substantially radial direction, a flat metallic strap secured at one end to said pivot within said cylinder and having at its other end a shoe slidably engaging said piston, said strap transmitting axial piston movement to turn said pivot and being free to bend as the distance between the piston and the pivot varies with changes in the axial position of the piston, and a connection between said pivot, externally of the cylinder, and said control mechanism to control fluid flow to the cylinder in response to certain positions of said piston.

4. In a controllable pitch propeller comprising hub and blades mounted therein, a pitch changing motor comprisin a piston rotatable with the propeller and connected with the blades and a non-rotating cylinder within which said piston is axially slidable, a hydraulic system connected to the cylinder operable to move said piston therein,

means turnably mounted in the wall of said cylinder having a portion engaged by said piston, whereby said means is turned in accordance with the axial position of said piston in the cylinder, a pitch limit stop element carried by said means and movable therewith, and a control device engageable with and actuatable by said element and controllably connected to said hydraulic system to control operation of said hydraulic system upon engagement of said element with said control device.

5. In a controllable pitch propeller comprising a hub and blades mounted therein, a pitch changing motor comprising a piston connected with the blades and a non-rotating cylinder within which said piston is axially slidable, a hydraulic system connected to the cylinder and operable to move the piston therein, a member journalled in the cylinder wall having an elastic strip secured thereto, said strip including a portion engaged and movable with the iston, whereby said member is rotated in accordance with the axial position of said piston, a pitch limit stop element carried by said member and movable therewith, and a control device engageable with and actuatable by said element and controllably connected to said hydraulic system to control operation of said hydraulic system upon engagement of said element with said control device.

MAURICE E. CUSHMAN.

Name Date Bishop et al. Apr. 25, 1933 Number Number Number 16 Name Date Harrington Sept. 17, 1940 Mader Oct. 1, 1940 Herman May 13, 1941 Herman et al Mar. 10, 1942 Mullen Jan. 12, 1943 Rindfleisch May 25, 1943 Martin Dec. 28, 1943 Keller July 11, 1944 Unterburg July 18, 1944 Stevenson Dec. 12, 1944 Stalker June 5, 1945 Kalin June 19, 1945 Keller Dec. 25, 1945 I-Iaines et al. Dec. 25, 1945 Cox Feb. 12, 1946 Martin Apr. 16, 1946 Hofbauer May 14, 1946 Kopp July 1, 1947 Haines July 29, 1947 Murphy et al. Aug. 5, 1947 Hoover Jan. 27, 1948 Wildhaber Feb. 1, 1949 Richardson et al. Apr. 25, 1950 FOREIGN PATENTS Country Date Italy June 10, 1938 Great Britain Mar. 20, 1940 Great Britain Apr. 6, 1944 

